Treatment advances during the past two decades in the treatment of CF have resulted in improved survival and center around preventing the loss of lung function. In 2005 the median predicted survival for people on the Cystic Fibrosis Foundation Patient Registry was 36.8 years and over 40% of all living people with CF are adults. The therapeutic treatment regimen, however, has evolved into a complex home treatment program that requires a substantial amount of patient commitment to perform and adherence to many components of CF treatment is often poor. While the regimen is efficacious in improving lung health and mortality, there is limited data on the level of adherence needed to maximize health outcomes. Similarly, there are few published adherence-promoting studies in CF and these have been limited to pediatric populations. Older adolescent and adult-focused interventions are therefore needed that target the unique challenges managing CF as one gets older and more independent. Motivational Interviewing (MI) is a promising interventional approach that uses a client-centered, non- directive approach for enhancing motivation to change health behaviors and has promising data as an effective adherence promoting intervention for adolescents and adults with other chronic illnesses. MI does not assume that health will be the most important factor motivating the client, but rather acknowledges and incorporates other motivators identified by the client. We propose to evaluate the efficacy of an Motivational Interviewing-focused intervention (MI) in improving adherence and reducing CF-related morbidity among older adolescents and adults compare to a standard CF education intervention (CFE; attention control group). Specifically, we hypothesize that MI will result in improved disease self-management and reduced CF morbidity compared to the CFE control group in a sample of 153 individuals with CF age 16+ years who are clinically stable at baseline. Our primary hypothesis is that participants receiving MI will have a higher composite medication adherence score at 12-months post-randomization (measured by pharmacy refill records) compared to the CFE group. Secondary outcomes include self-reported adherence, lung function (CF-specific percentiles of FEV1), pulmonary exacerbations, body mass index, and quality of life. This study will allow us to evaluate the longitudinal association between adherence and health outcomes. We will also evaluate the mediating effects of self-efficacy, motivation and CF knowledge on the intervention outcomes as well as moderator effects, such as age, autonomy, depression, social support, and life events.